Illumination devices based on semiconductor light sources, such as light-emitting diodes (LEDs), offer a viable alternative to traditional fluorescent, HID, and incandescent lamps. Functional advantages and benefits of LEDs include high energy conversion and optical efficiency, longer expected lifetime, lower operating costs, and many others.
There is a need for a remote controlled tunable LED-based white light source, wherein the correlated color temperature of the light source can be adjusted over a wide rage to meet a provide a desired characteristic which may be changed as a function of time, or from installation to installation or application to application. Often such tunable white light sources are built with several LEDs which emit primary colors, and one or more phosphor converted LED(s), and the light from all of these LEDs is combined to produce the desired white light. Red, Green, Blue and White devices are often used. In other White light sources, Red and Green LEDs are used together with a Cool-White LED and an Amber or phosphor-converted Amber (PCA) LED. Here, a remote controlled tunable LED-based white light source includes an LED-based white light source included in a lighting device meant for a wall dimmer.
As used herein, when referring to a device or LED as being a Red device or a Red LED, it is meant that the device or LED emits Red light. Similarly, a Blue device or Blue LED is one which emits Blue light, a Green device or Green LED is one which emits Green light, a White device or White LED is one which emits White light, etc. Furthermore, when referring to “a phosphor-converted LED”, it is meant an LED element having a phosphor material layer coated thereon for converting or changing the color of the light emitted by the LED element to a different color.
However, these known remote controlled tunable LED-based White light sources typically have a considerably lower efficiency than white light sources with a fixed correlated color temperature, so they require more energy and more LED elements to produce the same light output level. In particular, the use of Green LEDs in remote controlled tunable LED-based white light sources can result in a light source which exhibits a reduced efficiency compared to a “regular” white source. In general Green LEDs are less efficient than Blue LEDS, but Green LEDs can still supply quite a bit of light. However, since the Green light emitted by a Green LED is quite a distance in the color triangle away from the target (White) color, one needs to mix quite a bit Red light together with the Green light to get the desired White color. Furthermore, Red LEDs become inefficient at elevated temperatures. Reduced efficiency also means that more LEDs are required to achieve a desired light output level than would be required in a more efficient light source, thereby significantly increasing the cost and size of the light source.
Thus, it would be desirable to provide a remote controlled tunable correlated color temperature LED-based White light source which can operate efficiently and be tuned over a relatively wide color temperature range.